cis and trans sites of the TOM complex of mitochondria in unfolding and initial translocation of preproteins
- PMID: 9535859
- DOI: 10.1074/jbc.273.15.8806
cis and trans sites of the TOM complex of mitochondria in unfolding and initial translocation of preproteins
Abstract
Translocation of preproteins across the mitochondrial outer membrane is mediated by the TOM complex. Our previous studies led to the concept of two preprotein binding sites acting in series, the surface-exposed cis site and the trans site exposed to the intermembrane space. We report here that preproteins are bound to the cis site in a labile fashion even at low ionic strength, whereas intermediates arrested at the trans site remained firmly bound at higher salt concentration. The stability of the trans site intermediate results from interactions of both the presequence and unfolded parts of the mature part of the preprotein with the TOM complex. Binding to the trans site proceeded at rates comparable with those of unfolding of the mature domain and appeared to be kinetically limited by the unfolding reaction. Efficient binding to the trans site and unfolding were observed with both outer membrane vesicles and intact mitochondria whose membrane potential, DeltaPsi, was dissipated. Upon re-establishing DeltaPsi, trans site-bound preprotein resumed translocation into the matrix. The rates of unfolding and binding to the trans site were the same as those for translocation into intact energized mitochondria. We conclude that preprotein unfolding in intact mitochondria can take place without the involvement of the translocation machinery of the inner membrane and, in particular, the matrix Hsp70 chaperone. Further, preprotein unfolding at the outer membrane can be a rate-limiting step for formation of the trans site intermediate and for the entire translocation reaction.
Similar articles
-
Uncoupling of transfer of the presequence and unfolding of the mature domain in precursor translocation across the mitochondrial outer membrane.Proc Natl Acad Sci U S A. 1999 Mar 30;96(7):3634-9. doi: 10.1073/pnas.96.7.3634. Proc Natl Acad Sci U S A. 1999. PMID: 10097089 Free PMC article.
-
A dual role for mitochondrial heat shock protein 70 in membrane translocation of preproteins.J Cell Biol. 1993 Oct;123(1):109-17. doi: 10.1083/jcb.123.1.109. J Cell Biol. 1993. PMID: 8408191 Free PMC article.
-
Mitochondrial protein import. Tom40 plays a major role in targeting and translocation of preproteins by forming a specific binding site for the presequence.J Biol Chem. 1997 Jul 25;272(30):18725-31. doi: 10.1074/jbc.272.30.18725. J Biol Chem. 1997. PMID: 9228044
-
The mitochondrial import machinery for preproteins.Crit Rev Biochem Mol Biol. 2001;36(3):291-336. doi: 10.1080/20014091074200. Crit Rev Biochem Mol Biol. 2001. PMID: 11450972 Review.
-
Protein translocation into mitochondria.Biofactors. 1998;8(3-4):221-4. doi: 10.1002/biof.5520080308. Biofactors. 1998. PMID: 9914822 Review.
Cited by
-
The TOM complex is involved in the release of superoxide anion from mitochondria.J Bioenerg Biomembr. 2009 Aug;41(4):361-7. doi: 10.1007/s10863-009-9231-9. Epub 2009 Aug 19. J Bioenerg Biomembr. 2009. PMID: 19690949
-
Evidence of Distinct Channel Conformations and Substrate Binding Affinities for the Mitochondrial Outer Membrane Protein Translocase Pore Tom40.J Biol Chem. 2015 Oct 23;290(43):26204-17. doi: 10.1074/jbc.M115.642173. Epub 2015 Sep 2. J Biol Chem. 2015. PMID: 26336107 Free PMC article.
-
An internal targeting signal directing proteins into the mitochondrial intermembrane space.Proc Natl Acad Sci U S A. 1999 Oct 12;96(21):11752-7. doi: 10.1073/pnas.96.21.11752. Proc Natl Acad Sci U S A. 1999. PMID: 10518522 Free PMC article.
-
Tom40, the import channel of the mitochondrial outer membrane, plays an active role in sorting imported proteins.EMBO J. 2003 May 15;22(10):2380-6. doi: 10.1093/emboj/cdg229. EMBO J. 2003. PMID: 12743032 Free PMC article.
-
Dynamics of the TOM complex of mitochondria during binding and translocation of preproteins.Mol Cell Biol. 1998 Sep;18(9):5256-62. doi: 10.1128/MCB.18.9.5256. Mol Cell Biol. 1998. PMID: 9710610 Free PMC article.
Publication types
MeSH terms
Substances
LinkOut - more resources
Full Text Sources
Molecular Biology Databases
